Neutrino Astrophysics

Peter Mészáros, Irina Mocioiu, Shan Gao

The same shocks which the electrons responsible for the non-thermal gamma-rays in
GRB should also accelerate protons present in the shockis. Both the internal
and the external reverse shocks are mildly relativistic, and are expected to lead
to relativistic proton energy spectra of the form E^{-2}.
For this, the acceleration time must be shorter than both the radiation or
adiabatic loss time and the escape time from the acceleration region. The same
constraints on the magnetic field and the bulk Lorentz factor required to obtain
efficient electron acceleration and gamma-ray emission at ~1 MeV indicate that
the protons reach Lorentz factors ranging up to 10^{11}. This makes them potential
cosmic ray sources.
The accelerated protons in the GRB jet can interact with the fireball photons, leading
to charged pions, muons and neutrinos. This reaction peaks at the energy threshold
for the photo-meson Delta resonance. For internal shocks producing observed 1 MeV
photons this implies ~ 10^{16} eV protons, and neutrinos with ~ 5 % of that energy,
E_nu ~ 10^{14} eV. Above this threshold, the fraction of the proton energy lost
to pions is ~ 20% for typical fireball parameters, and the typical spectrum of
neutrino energy per decade is flat, E_nu^2 Phi_nu ~ constant (Waxman & Bahcall, 1997).
Synchrotron and adiabatic losses limit the
muon lifetimes
(Rachen & Meszaros 1998), suppressing the neutrino flux above E_nu ~ 10^{16} eV.
Another copious source of target photons in the UV is the afterglow reverse shock,
for which the resonance condition requires higher energy protons leading to neutrinos of
10^{17}-10^{19} eV (Waxman & Bahcall, 1999). These neutrino fluxes are expected
to be detectable above the atmospheric neutrino background with the planned cubic
kilometer ICECUBE Cherenkov detector,
Penn State being involved in the science
and data analysis aspects. IceCube construction is finished (2011), including
its ``Deep Core" array for measuring down to 10-15 GeV energies.

Another mechanism for neutrino production in GRB is inelastic nuclear collisions.
Provided the fireball has a substantial neutron/proton ratio, as expected in most
GRB progenitors, the inelastic process is most intense when the nuclear scattering
time scale becomes comparable to the expansion time scale, at which point the relative
velocities of the nuclei become large enough to collide inelastically, resulting in
charged pions and
~few GeV neutrinos (Bahcall & Meszaros 2000). Inelastic collisions can also
occur in fireball outflows with transverse inhomogeneities in the bulk Lorentz factor
(Meszaros & Rees 2000). The typical neutrino energies are in the
10 GeV range , which could be detectable with the IceCube Deep Core array
in coincidence with nearby observed GRBs (see also Meszaros & Rees (2011).

The photo-pion and inelastic collisions responsible for the ultra-high energy
neutrinos will also lead to neutral pions and electron-positron pair cascades,
resulting in GeV to TeV energy photons. A tentative ~ 0.1 TeV detection of a GRB
has been reported
(Atkins et al 2001) with the water Cherenkov detector Milagrito, protoptype of
MILAGRO . Other large atmospheric
Cherenkov detectors, as well as space-based large area solid state detectors such
as on FERMI are able to measure photons
in this energy range, which would be coincident with the neutrino pulses and the
usual MeV gamma-ray event. Their detection would provide important constraints on
the emission mechanism of GRBs. GeV emission is also a feature of many AGNs, in
particular blazars. For jets with high jet Lorentz factors and small inclination
to the observer, photons out to ~10 TeV have been measured with ground air
Cherenkov telescopes. In such cases, a secondary
reprocessed GeV photon halo
may be detectable, from inverse Compton scattering on CMB photons by pairs
produced in TeV-IR photon-photon interactions
(Dai, Zhang, Gou, Meszaros & Waxman, 2002).

A potentially important source of high energy neutrinos in GRB is expected in
collapsar models. The core collapse of massive stars resulting in a relativistic
jet which breaks through the stellar envelope is a widely discussed scenario for
gamma-ray burst production. For very extended or slow rotating stars,
the jet may be unable to break through the envelope. Both
penetrating and choked jets (Meszaros & Waxman 2001)
will produce, by photo-meson interactions of accelerated
protons, a burst of ~3-5 TeV neutrinos while propagating in the stellar envelope.
The predicted flux, from both penetrating and choked jets, should be easily
detectable by planned cubic kilometer neutrino telescopes. The contribution of
pp collisions between
accelerated jet protons and stellar envelope nucleons gives a more prominent
TeV component (Razzaque, Meszaros & Waxman 2003b).

High energy neutrinos may also be produced in
magnetars, which are
ultra-high magnetic field neutron stars that can accelerate cosmic rays
to high energies through the unipolar effect, as well as being copious soft
X-ray emitters. Zhang, Dai, Meszaros & Waxman (2002) show that young,
fast-rotating magnetars should emit TeV neutrinos through photomeson interactions.
An exciting possibility is that the recent giant flare of the Soft Gamma Repeater
SGR 1806-20 recently detected (December 28 2005) in gamma-rays by Swift may
also produce cosmic rays and neutrinos. Ioka, Razzaque, Kobayashi and Meszaros
calculated the TeV neutrino
flux expected from this SGR. Proton acceleration and p,gamma interactions
would produce signals detectable with AMANDA for a high enough baryon load fireball,
and analysis of dat taken by Amanda II are underway. This emission would be associated
also with detectable TeV gamma-ray emission.

Long Gamma-Ray Bursts (lasting longer than ~10 s) are also sometimes found
associated with a supernova, which is of interest for the X-ray and optical
afterglow, as well as for constraining progenitor scenarios. A test of the
presence of such a SNR shell preceding the GRB explosion, as in the supranova
scenario, would lead to distinctive neutrino spectra in the
TeV range (Razzaque, Meszaros and Waxman 2003a).
Razzaque, Meszaros and Waxman calculated in detail the neutrino detection
prospects from a nearby GRB such as GRB030329 by a km scale detector such
which ICECUBE should be able to detect.

Alvarez-Muniz and Meszaros (2004) developed a quantitative model of
radio-quiet AGNs
as sources of cosmic rays and high energy neutrinos, related to
X-ray emission models. These sources, which do not have significant jets, may
be ten times more numerous than blazars, and hence may be important
ICECUBE candidates.

Razzaque, Meszaros and Waxman (2005) investigated the possibility of
semi-relativistic jets being present in
core collapse supernovae
which are not related to GRB, as suggested by anisotropic, polarized remnant
observations. Proton acceleration in shocks in these incipient jets
could lead to neutrino emission detectable with ICECUBE out to 20 Mpc.

Ioka, Kobayashi and Meszaros (2005) interpreted the anisotropic supernova remnant
W49B as the result of
a collapsar gamma-ray burst, where proton acceleration
leads to neutrons decaying far from the remnant. The decay electrons lead
to inverse Compton which results in GeV-TeV photons, with a flux which could in
principle be detectable with FERMI and ground-based air Cherenkov telescopes.

As part of the ICECUBE collaboration, Meszaros and Razzaque calculated
models and participated in the evaluation of the
sensitivity
of this detector to high energy muon neutrinos from specific sources, as well
as on an evauation of the first year
performance of ICECUBE .

Neutron-rich material in both short and long GRB is expected to be ejected
by the central engine. The free neutrons beta decay to a proton, an electron
and an anti-neutrino in about fifteen minutes in its rest frame. The sudden
creation of a relativistic electron is accompanied by radiation with
unique temporal and spectral signature. Razzaque and Meszaros calculated this
radiation signature collectively emitted by all
beta decay electrons
from neutron-rich outflow. Detection of this signature, e.g. by FERMI, may thus
provide strong evidence for not only neutron but also for proton
content in the relativistic gamma-ray burst jets.

The ratio of anti-electron to total neutrino flux, expected from p,gamma
interactions in astrophysical sources is generally 1:15. However this ratio is
enhanced by the decay of muon-antimuon pairs, created by the
annihilation of secondary high energy photons from the decay of the
neutral pions produced in p,gamma interactions. Razzaque, Meszaros and Waxman
(2006) showed that the
anti-electron to total neutrino ratio may be
significantly enhanced in gamma-ray burst (GRB) fireballs, and that
detection at the Glashow resonance of $\bar{\nu}_e$ in kilometer scale
neutrino detectors may constrain GRB fireball model parameters, such
as the magnetic field and energy dissipation radius.

The afterglow emission from short gamma-ray bursts suggests that binary neutron star
or NS-BH mergers may be the progenitors. Razzaque and Meszaros (2006) considered a
neutron-rich relativistic jet model of short bursts, which predicts a high energy neutrino
and photon emission as neutrons and protons decouple. Upcoming neutrino telescopes
are unlikley to detect the 50 GeV neutrinos expected in this model, but for bursts
at z~0.1, FERMI and ground-based Cherenkov telescopes should be able to detect prompt
100 MeV and 100 GeV photon
signatures, which may help test the progenitor identification.

Young magnetars may be born with milisecond rotation periods, and the ultrastrong
magnetic field will result in a Poynting dominated outgoing wavefield, which
can accelerate cosmic rays to GZK energies through wake-field acceleration.
In this case, one could probe the birth of
fast rotating magnetars through high-energy neutrinos,
(Murase, Meszaros and Zhang, 2009), which are produced when the hultra-high
energy protons interact with the ejected outer stellar envelope (the supernova
remnant).

An interesting direct generation mechanism of production of
High Energy Neutrinos and Photons from Curvature Pions in Magnetars was
investigated by Herpay, Razzaque, Patkós and Mészáros.
This is expected through the curvature radiation of pions in strongly magnetized
pulsars or magnetars. This mechanism operate only in magetars, since it requires
the very high fields measured in these objects. The production of TeV energy
neutrinos associated with this is expected to be detectable by cubic kilometer
scale detectors, while the high energy photons are in the range of space detectors.

With graduate student Shan Gao and postdoc Kenji Toma (2011) we studied
the properties of very high redshift (10 Pop. III GRBs
have a very hard neutrinos spectrum, PeV to EeV, and they could be detected by
IceCube in 5 years. The figure on the right is for a 300 solar mass object.

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